[llvm] [flang-rt] Add support for using LLVM in-tree libc/libc++ (PR #131695)

[Daniel Chen via llvm-commits]

DanielCChen wrote:

> [60eb89f](https://github.com/llvm/llvm-project/commit/60eb89f9fa0fd990c5cf2cc64d4202e3485d256e) should fix it.

@jhuber6 Thanks for the quick response!

https://github.com/llvm/llvm-project/pull/131695